CDL General Knowledge — All Questions

A car pulls out directly in front of you and there is not enough distance to stop. What is generally the best response?

• a.Downshift and hope the gap clears
• b.Sound the horn and maintain speed
• c.Brake as hard as possible and hold the pedal down
• d.Steer around the hazard if there is an escape path, because a vehicle can change direction faster than it can stop✓

Stopping distance grows with the square of speed, but the time needed to steer around an obstacle changes very little, so an evasive steer is often the only option that works. Locking the brakes destroys steering control, the horn does not shorten the closing distance, and downshifting is far too slow to help.

You are traveling at highway speed when a front tire blows out. What should you do first?

• a.Brake hard immediately
• b.Accelerate to regain control
• c.Hold the steering wheel firmly, stay off the brake, and let the vehicle slow on its own before easing to the shoulder✓
• d.Steer sharply onto the shoulder

Braking on a blown tire pulls the vehicle sharply toward the failed side, so you must keep it straight and let it slow before braking gently and pulling off. Sharp steering can roll the vehicle, and accelerating adds energy to an already unstable situation.

How can you tell that a tire has failed if you did not hear the blowout?

• a.The fuel gauge drops rapidly
• b.The air pressure gauge reads zero
• c.A thumping or vibration, a sudden change in steering feel, or the rear of the vehicle fishtailing✓
• d.The engine loses power

Vibration, a pull in the steering when a front tire fails, or a fishtailing rear when a rear tire fails are the usual clues. Tire failure does not affect fuel level, brake system air pressure, or engine power.

Your right wheels drop off the pavement onto a soft shoulder at 55 mph. What is the correct recovery?

• a.Steer back onto the pavement while maintaining speed
• b.Keep a firm grip, stay off the brake and take your foot off the accelerator, let the vehicle slow, then turn back onto the pavement sharply at low speed✓
• c.Accelerate to power back onto the road
• d.Brake hard and steer left immediately

Trying to climb back onto the pavement at speed can throw the vehicle across the road or into a rollover, so you slow first and then make a deliberate sharp return. Hard braking on a soft shoulder can cause a skid, and accelerating increases the speed at which you re-enter the lane.

Your air brakes fail on a downgrade and the low-pressure warning is on. What is your best course of action?

• a.Downshift to use engine braking, look for an escape ramp or an uphill escape route, and use the parking brake or a soft-shoulder route as a last resort✓
• b.Pump the brake pedal rapidly to rebuild pressure
• c.Shut off the engine to stop the vehicle
• d.Shift to neutral so the vehicle rolls more freely

Engine braking and an escape ramp are the reliable tools once the service brakes are gone, and speed must be controlled before it becomes uncontrollable. Pumping air brakes wastes remaining pressure, neutral increases speed, and shutting off the engine removes power steering and engine braking together.

Which type of fire extinguisher should you use on an electrical fire in the cab?

• a.A pressurized garden hose
• b.Any extinguisher, as long as it is full
• c.A water extinguisher
• d.A B:C rated extinguisher such as dry chemical or carbon dioxide✓

Electrical fires are Class C, so the agent must be non-conductive, which is why a B:C or A:B:C rated dry chemical or carbon dioxide unit is required. Water conducts electricity and can electrocute the user or spread the fire, and choosing an extinguisher by fullness alone ignores the class rating.

A grease or fuel fire starts near the engine. Why must you never use water on it?

• a.Water damages the paint
• b.Water freezes on hot metal
• c.Water is too heavy to carry
• d.Water spreads burning liquid instead of putting it out✓

Burning liquids float on water, so a stream of water scatters the fire over a larger area. Weight, freezing, and paint damage are irrelevant compared with the danger of spreading a Class B fire.

You are using a fire extinguisher on a small cargo fire. What is the correct technique?

• a.Stay upwind, position yourself about 6 to 10 feet away, pull the pin, aim at the base of the fire, and sweep side to side✓
• b.Empty the extinguisher into the smoke above the fire
• c.Stand as close as possible and aim at the top of the flames
• d.Approach from downwind so the wind carries the agent in

Aiming at the base attacks the fuel source, and staying upwind and back keeps you clear of heat and fumes. Standing too close, spraying smoke, or approaching from downwind exposes you to the fire and wastes the extinguisher's limited charge.

What is the minimum fire extinguisher rating required on a vehicle transporting hazardous materials that requires placards?

• a.No extinguisher is required if the load is non-flammable
• b.Two 2 B:C extinguishers
• c.A single extinguisher with a rating of at least 10 B:C✓
• d.A single 5 B:C extinguisher

Placarded hazardous materials vehicles must carry an extinguisher rated at least 10 B:C, while other commercial vehicles need at least a 5 B:C or two units rated 4 B:C each. Smaller units do not meet the hazmat standard, and every commercial vehicle needs an extinguisher regardless of the cargo.49 CFR §393.95

You are the first vehicle at the scene of a crash on a rural highway. What is the correct order of priorities?

• a.Take photographs first for the insurance claim
• b.Move all injured people off the roadway immediately, then call for help
• c.Leave the scene to find a phone with better signal
• d.Protect the area so no further crashes occur, notify authorities, then care for the injured✓

Preventing a second collision protects both you and the people already involved, and emergency services are needed before hands-on care. Moving injured people risks worsening spinal injuries unless fire or another danger is present, and photographs or leaving the scene delay the response.

You have just left the shipper with a secured load. When must you first re-inspect the cargo and its securement?

• a.Within the first 50 miles of the trip✓
• b.After 500 miles
• c.Only if the load shifts noticeably
• d.Only at the destination

The rule requires an inspection within the first 50 miles, then a re-examination every 150 miles or every 3 hours of driving, whichever comes first. Waiting until the destination, 500 miles, or a noticeable shift means the securement has already failed.49 CFR §392.9

What is the minimum aggregate working load limit for the tiedowns securing a piece of cargo?

• a.At least 50 percent of the weight of the cargo being secured✓
• b.There is no numeric requirement
• c.100 percent of the weight of the cargo
• d.25 percent of the weight of the cargo

The combined working load limit of all tiedowns must equal at least half the weight of the article being secured. Twenty-five percent is below the standard, requiring 100 percent overstates the rule, and the requirement is clearly numeric.49 CFR §393.106

You are securing a single 12-foot pipe weighing 1,800 pounds on a flatbed. How many tiedowns are required at minimum?

• a.Two tiedowns
• b.Three tiedowns✓
• c.One tiedown
• d.Four tiedowns

An article longer than 10 feet needs two tiedowns for the first 10 feet plus one more for each additional 10 feet or fraction, so a 12-foot article needs three. One tiedown is only allowed for articles 5 feet or shorter and 1,100 pounds or less, and four exceeds the minimum for this length.49 CFR §393.110

Your load is stacked high in a van trailer with the heaviest cases on top. Why is this dangerous?

• a.It makes the trailer harder to unload
• b.It causes the trailer brakes to overheat
• c.A high center of gravity makes the vehicle much more likely to roll over in a curve or in a sudden maneuver✓
• d.It increases fuel consumption

Heavy weight placed high raises the center of gravity, and rollover risk climbs sharply in curves, on ramps, and during evasive steering. Unloading effort, fuel use, and brake temperature are minor compared with the stability problem.

What is the maximum gross vehicle weight generally allowed on the Interstate highway system without a special permit?

• a.60,000 pounds
• b.100,000 pounds
• c.70,000 pounds
• d.80,000 pounds✓

The federal limit is 80,000 pounds gross, with 20,000 pounds on a single axle and 34,000 pounds on a tandem axle set, subject to the bridge formula. Sixty and seventy thousand are below the legal maximum, and 100,000 pounds requires a permit.

You are scaled at 21,000 pounds on the steer axle and 33,000 pounds on the drive tandem. What is the problem?

• a.The drive tandem exceeds the tandem limit
• b.Nothing is wrong because the gross weight is legal
• c.Both axle groups are over the limit
• d.The single steer axle exceeds the 20,000 pound federal limit and weight must be shifted✓

A single axle is limited to 20,000 pounds, so 21,000 is overweight even though the tandem at 33,000 is under the 34,000 pound limit. A legal gross weight does not excuse an overloaded individual axle, and only the steer axle is over here.

You are hauling a placarded load of flammable liquid. Where must the shipping papers be kept while you are driving?

• a.In the sleeper berth
• b.Locked in the trailer with the cargo
• c.Within the driver's immediate reach while the seat belt is fastened, and clearly visible or in a pouch on the driver's door✓
• d.Emailed to the carrier is sufficient

Emergency responders must be able to find the papers quickly, so they must be within reach and identifiable from the driver's side. Papers in the trailer, in a sleeper, or only in electronic form at the office are unavailable to responders at the scene.

What is the primary purpose of hazardous materials placards on a commercial vehicle?

• a.To warn the public and emergency responders of the class of hazard on board✓
• b.To indicate the value of the cargo
• c.To identify the shipper and consignee
• d.To show the vehicle's insurance coverage

Placards communicate the hazard class so responders can select the correct tactics before approaching the vehicle. They do not identify the parties to the shipment, the cargo value, or the insurance.

A tire on your trailer catches fire at a rest area and you have a 10 B:C extinguisher. What is the realistic limitation you must plan for?

• a.The extinguisher will smother the tire fire in a few seconds
• b.A burning tire holds heat deep inside and usually needs large amounts of water, so the extinguisher may only slow it while you keep people away and call the fire department✓
• c.Dry chemical is prohibited for use near tires
• d.Tire fires go out on their own once the vehicle stops

Tires reignite because the fire burns inside the casing where a dry chemical agent cannot reach, so the priority is evacuation and calling for help. Tire fires do not self-extinguish, and dry chemical is not prohibited, it is simply not sufficient.

You pull into a rest area and smell fuel and see smoke from under the hood. What should you do?

• a.Continue driving to the nearest repair shop
• b.Shut off the engine, get yourself and any passengers away from the vehicle, and use the extinguisher only if the fire is small and you can do so safely✓
• c.Spray water on the engine compartment
• d.Open the hood fully to see the source

Cutting the fuel and ignition source and keeping people clear are the first priorities, and extinguishers are only for small, contained fires. Opening the hood feeds oxygen to the fire, driving fans the flames, and water on a fuel fire spreads it.